With the advent of the waterbed mattress, conventional designs for form-fitted bed sheets which securely cover a mattress has been modified, in order to accommodate the more loose form of a waterbed mattress in comparison to the more rigid form of an innerspring mattress. Such construction has required either a corner pocket panel or an elongated head or foot panel which is comprised of an elasticized material such as, for example, tricot. The pocket corner or panel fits underneath the sleeping surface of the waterbed and prevents the form-fitted sheet from coming loose from the waterbed mattress.
It is convention in the industry that waterbed mattresses and innerspring mattresses for the same size classification (e.g., king size, queen size) are of different dimensions. For example with a king size mattress classification, a standard innerspring mattress is generally 76 inches wide and 80 inches long and 6 or more inches thick. In comparison, a king size waterbed mattress is generally 72 inches wide and 84 inches long. Thus, in order for retailers to sell to both of these markets, there is a requirement that they carry two distinct types of bedding, one to satisfy the dimensional and form requirements of a waterbed and one to satisfy the dimensional and form requirements of an innerspring mattress. Given the fact that there are a number of size classifications for mattresses, the amount of inventory that a retailer has to carry is substantial.
There are several prior art references which use wedge inserts and corners designed into fitted bed sheets. For example, Shaver, U.S. Pat. No. 2,162,755, teaches a fitted sheet which has a triangular gusset made of material which is somewhat heavier than the material from which the sheet itself is made. The gusset can accommodate a certain amount of pulling without tearing and can be comprised of elastic material, knitted fabric or the like. Such a gusset as described in this patent does not allow the bed sheet to conform to waterbed and innerspring mattresses which can have vastly different dimensions for the same size classification.
The Harris patent, U.S. Pat. No. 2,624,893 discloses a mattress covering which has corners comprised of a flat knit material having spaced elastic threads inserted therein. The corner inserts are triangular in shape. The pocket portion formed under the mattress would not hold the sheet onto a waterbed mattress and the material contemplated by Harris would not have sufficient stretchability to cover the various dimensions for any size classification for waterbed and innerspring mattresses.
Accordingly, there is a need to provide a design for a single fitted sheet which will accommodate, for any given size classification, the different dimensions and form requirements of a waterbed mattress as well as an innerspring mattress in order to reduce the retailer's inventory requirements.